Device to Device communication occurs when devices such as user equipment (UE) communicate user data with each other directly without the user data being transmitted via a higher level network node such as a eNodeB. In such device to device communication two or more user equipment are provided with a resource pool containing resources that may be used for device to device communication. A UE initiating the device to device communication may send a scheduling assignment to a further UE indicating the resources of the pool that have been scheduled for communication between the UEs.
In a first mode of device to device communications, the resources may be scheduled by an access node. A transmitting UE (Tx UE) may request that a network node schedules resources for the communication and then provide an indication of the scheduled resources to a receiving UE (Rx UE). In this manner both the transmitting and receiving UEs are aware of the scheduling for the device to device communication. In a second mode, a transmitting UE may autonomously use or schedule the resources. The transmitting UE may indicate the scheduled resources to the receiving UE. In this manner both the transmitting and receiving UEs are aware of the scheduling for the device to device communication.
The first mode of device to device communication may be implemented where the transmitting UE is in a coverage area of the access node that schedules the resources. The second mode of device to device communication may be implemented in cases where the transmitting UE is outside or within the area of coverage of an access node however typically the transmitting UE will be outside the coverage area for the second mode. The transmitting UE may determine whether the device to device communication will be in accordance with the first mode or with the second mode, under pre-configuration and control of the serving network.
In device to device communication, a receiving UE may be aware of a resource or pool of resources on which the transmitting UE may transmit the scheduling assignment for device to device communication. The receiving UE may monitor this resource or pool of resources for the scheduling assignment. This monitoring may use energy and processing resources of the UE.